CN114920536A

CN114920536A - Ultra-high performance concrete microcrack repairing agent

Info

Publication number: CN114920536A
Application number: CN202210351298.5A
Authority: CN
Inventors: 陈波; 郭丽萍; 孙仁杰; 王雄锋; 吕乐乐; 张丰; 白银; 宁逢伟
Original assignee: Nanjing Hydraulic Research Institute of National Energy Administration Ministry of Transport Ministry of Water Resources
Current assignee: Nanjing Hydraulic Research Institute of National Energy Administration Ministry of Transport Ministry of Water Resources
Priority date: 2022-04-02
Filing date: 2022-04-02
Publication date: 2022-08-19

Abstract

The invention discloses an ultra-high performance concrete microcrack repairing agent, which comprises the following components in parts by weight: 1-2 parts of sodium metaaluminate or sodium aluminate, 100-150 parts of silica sol, 3-5 parts of wetting agent and 100-150 parts of water; wherein the wetting agent is an organic fluorine wetting agent and is one or more of F3030, F3025 and F140. Has the advantages that: the silica particles in the silica sol repair agent of the invention can be bound together by different coagulation mechanisms, such as gelation and flocculation. Under the gelling action, the silanol groups on the surfaces of the colloidal particles are subjected to dehydration condensation to form siloxane, and then a three-dimensional network structure is formed. Meanwhile, under the catalytic action of sodium aluminate, the reaction with calcium hydroxide in concrete is accelerated, calcium silicate is generated, and the calcium silicate is used as a repair product, so that cracks can be filled, and the mechanical properties such as bending strength, ductility and the like of the slotted HDCC are improved.

Description

Ultra-high performance concrete microcrack repairing agent

Technical Field

The invention relates to the technical field of concrete repair, in particular to an ultra-high performance concrete microcrack repairing agent.

Background

Concrete constructions are prone to cracking due to additional loads and environmental exposure. Cracking of cement-based materials is a difficult problem to avoid because it not only causes a reduction in the load-bearing capacity and durability of concrete, but also may be expanded, resulting in a serious safety accident. In general, cracks are mainly classified into surface cracks and internal cracks. Surface cracks can aggravate the erosion of harmful substances to the concrete, and internal cracks can reduce the mechanical strength of the concrete. High-ductility concrete (HDCC) has better "ductility" than ordinary concrete. However, high ductility concrete generates many fine cracks when it is subjected to tensile stress. The existence of micro-cracks affects the mechanical properties of high ductility concrete. The influence degree is determined by the depth and the width of the microcracks, when the width of the microcracks is less than 60 mu m, the mechanical property is hardly influenced, and therefore, the repairing is not necessary, and when the width of the microcracks is more than 60 mu m, the mechanical property, particularly, the tensile strength and the bending strength are influenced, so that the improvement of the service performance of the high-ductility concrete by using the repairing agent to repair the microcracks with the width of more than 60 mu m in the high-ductility concrete has a wide prospect. At present, the common repairing methods include grouting methods, including grouting repairing materials such as nail set and propyl set, and prestressed repairing methods. These methods do not have obvious effect on the microcracks in high ductility concrete because many microcracks are difficult to repair, and particularly when the width of the microcracks is below 200 μm, the repair material is difficult to penetrate deep into the cracks for repair. Moreover, the appearance of the product is not beautiful after the repair is completed, and thus, the safety of the project is worried. Therefore, it is necessary to develop a new concrete repair agent with high ductility.

Disclosure of Invention

The invention aims to overcome the technical defects and provide the ultra-high performance concrete microcrack repairing agent which is reasonable in structure, strong in practicability and good in using effect.

In order to solve the technical problems, the technical scheme provided by the invention is as follows: an ultra-high performance concrete microcrack repairing agent, HDCC microcrack repairing agent material according to the part by weight, includes the following components: 1-2 parts of sodium metaaluminate or sodium aluminate, 100-150 parts of silica sol, 3-5 parts of wetting agent and 100-150 parts of water; wherein the wetting agent is an organic fluorine wetting agent and is one or more of F3030, F3025 and F140.

Further, the specific preparation method comprises the following steps:

a: mixing part of water, a sodium aluminate solution and silica sol to obtain a primary mixed material, wherein the used parts by weight of the part of water in the primary mixed material are the same as the parts by weight of the silica sol, the mixing sequence is not limited at all, the mixing is carried out under the stirring condition, the stirring rotating speed is initially set to be 500-1500 r/min, is preferably 800-1200 r/min step by step and is finally determined to be 1000 r/min; the stirring time is initially 15-50 min, preferably 20-40 min gradually, and finally determined to be 25-35 min; after stirring, standing the obtained mixture; standing for 15-25 min initially, and in the stirring process, reacting sodium aluminate in the initial mixed material with silicon dioxide in the silica sol to generate aluminum-containing silicate;

b: after the initial mixed material is obtained, mixing the residual water and the wetting agent, wherein the sum of the weight part of the residual water and the weight part of the water is the weight part of the water in the technical scheme; the rotation speed of stirring is initially set to be 100-300/min, and the preferred rotation speed is 200 r/min; the stirring time is preferably 10-15 min, after the stirring is finished, the obtained mixture is kept still, and the standing time is preferably 18-22 min;

c: after standing, mixing the primary mixed material and the standing material to obtain the HDCC microcrack repairing agent, wherein the mixing is carried out under the stirring condition, the stirring rotating speed is initially 500-1000/min, and the optimal selection is gradually 600-800 r/min; the stirring time is 5-20 min initially, and is preferably 10-15 min gradually

d: the HDCC microcrack repairing agent is used, the HDCC microcrack repairing agent is uniformly coated on a position to be repaired of concrete, and the condition that obvious effusion cannot exist on a coating surface is ensured; the coating times are 2-6; after the coating is finished, the coated position is guaranteed not to be stained with water within 24 hours, and within the time range of 24 hours, the active ingredients of the HDCC microcrack repairing agent generate self-crosslinking reaction to repair cracks.

Compared with the prior art, the invention has the advantages that: (1) the repair mechanism of the epoxy resin repair agent in the prior art is that the epoxy resin repair agent plays a role in bonding in cracks, and new reaction products cannot be generated to fill the cracks; the silica particles in the silica sol repair agent of the present invention can be bound together by different coagulation mechanisms, such as gelation and flocculation. Under the gelatinization, the silanol groups on the surfaces of the colloidal particles are subjected to dehydration condensation to form siloxane, and then a three-dimensional network structure is formed. Meanwhile, under the catalytic action of sodium aluminate, the reaction with calcium hydroxide in concrete is accelerated, calcium silicate is generated, and the calcium silicate is used as a repair product, so that cracks can be filled, and the mechanical properties such as bending strength, ductility and the like of the HDCC with the cracks are improved.

(2) After the HDCC sample with the crack is coated with the silica sol repairing agent, the silica sol repairing agent can quickly permeate into the crack and generate self-crosslinking reaction, and a repairing product calcium carbonate is generated to fill the crack. After the HDCC sample with the crack is coated with the epoxy resin repairing agent, the crack still exists, the width of the crack does not change obviously, and the main mechanism of the epoxy resin repairing agent repairing is that the epoxy resin glue solution plays a role in bonding in the crack, and a new repairing product is not generated to fill the crack.

(3) For a plurality of micro cracks with the width of 60-150 mu m in the HDCC, the penetration depth of the silica sol repairing agent is better than that of the epoxy resin repairing agent, and a repairing product can be generated to fill the cracks, the repairing effect is better than that of the epoxy resin repairing agent, and for the cracks with the width of more than 150 mu m, the epoxy resin repairing agent can also penetrate into the depths of the cracks and can play a role in bonding, and the repairing effect is better than that of the silica sol repairing agent.

Drawings

FIG. 1 is a diagram of a four-point bend test setup.

FIG. 2 is a crack signature of HDCC bent specimens.

FIG. 3 shows the fracture morphology (magnification 50 times) of a limit deflection HDCC sample.

Fig. 4 is a pre-load level 50% HDCC specimen fracture morphology (50 x magnification).

FIG. 5 is a side view X-CT tomographic scan of group A samples.

FIG. 6 is an elevational X-CT tomographic scan of group A samples.

FIG. 7 is a side view X-CT tomographic scan of a group B of samples.

FIG. 8 is an elevational X-CT tomographic scan of a group B sample.

Figure 9 is a four set sample XRD pattern.

Fig. 10 is a FTIR spectrum for four sets of samples.

FIG. 11 is a plot of the cracks in group A samples (50X magnification).

FIG. 12 is a plot of the fracture morphology (50 times magnification) for the group B samples.

FIG. 13 is a side view of an X-CT tomographic scan of a group A sample after its repair.

FIG. 14 is an elevational view of a set A of specimens after repair.

FIG. 15 is a side view X-CT tomographic scan of a group B specimen after repair.

FIG. 16 is an elevational X-CT tomographic scan of group B samples after their repair.

Detailed Description

The following further describes embodiments of the present invention with reference to the accompanying drawings.

The high-ductility concrete HDCC serving as one of fiber reinforced cement-based composite materials has good crack control capacity, and is prepared by purposefully adjusting fiber characteristics, matrix characteristics and fiber-matrix interface characteristics on the basis of micro-mechanics and fracture mechanics. HDCC (PVA-HDCC) with the polyvinyl alcohol fiber volume mixing amount of 2% has an obvious strain hardening process under uniaxial tensile load and is accompanied with multi-crack cracking, and the crack width can be stably controlled below 150 mu m.

HDCC not only has good mechanical properties, but also has unique crack control capability: when the HDCC bears the tension-bending load and the fatigue load, the fibers can effectively resist cracking, bridge cracks and transmit stress, so that multi-crack cracking is realized, and the strain hardening behavior similar to that of a metal material is shown. This unique crack control capability is also an important reason for the good mechanical properties of HDCCs.

Various shrinkage stresses (drying shrinkage, temperature shrinkage and carbonization shrinkage) exist in the hardened cement-based material, the incorporation of fibers prevents the propagation of microcracks due to stress concentration and prevents the occurrence of connected cracks, and HDCC enables multi-crack cracking with crack widths maintained below 50 μm under shrinkage-limiting conditions. The strain hardening characteristic and the multi-crack cracking process of the HDCC are very stable under the action of direct tensile load, the crack width of the HDCC with the ultimate elongation of 1.5-5% can be controlled to be below 150 mu m, and the crack spacing is below 10 mm. The ductility and crack control ability of HDCC will deteriorate with time, but the final crack width can still be controlled below 150 μm and the spacing is in the millimeter level.

The existing methods for treating and repairing the cracks by using the cement-based structural material are mainly divided into post repair and self repair, and the repair method and the repair material are mainly determined according to various influence factors such as the basic function of the structure, the cracking reason, the shape of the cracks, the importance of the structure, the condition of the environment where the cracks are located and the like. The self-repairing mechanism is mainly to artificially trigger a healing agent, such as microencapsulated bacteria or crystal admixtures and the like. Microcapsule repair is carried out by suspending water-soluble monomer phase in non-polar organic solvent n-hexane, forming small droplets by stirrer and surfactant, and polymerizing at high temperature. The disadvantage of microcapsule repair is that the shell characteristics of the microcapsules have a significant effect on the observed healing efficiency, and studies have shown that the addition of the span 60 emulsifier adds a hydrophobic coating to the shell of the microcapsules, increasing the likelihood of agglomeration due to hydrophobic attraction between the microparticles, which results in a non-uniform dispersion of the capsules throughout the concrete matrix of the concrete sample.

Another self-healing method is the crystal admixture repair, namely after the active chemical substances contained in the cement-based permeable crystalline waterproof material (CCCW) interact with water, the water is used as a carrier to permeate into the concrete to generate water-insoluble acicular crystals and cement hydration products, thereby filling capillary pores and microcracks and improving the compactness and the waterproofness of the concrete. The self-healing mechanism is primarily that the sodium aluminate contained in the CCCW contributes to the formation of ettringite and sodium hydroxide in the cement. Sodium hydroxide accelerates the absorption of carbon dioxide, forming carbonate ions, and thus calcium carbonate formation. Meanwhile, the EDTA tetrasodium in the CCCW is also attached to the calcium carbonate crystal, so that the shape of the calcium carbonate crystal is changed, the length-diameter ratio of the calcium carbonate crystal is greatly improved, and the calcium carbonate crystal with high length-diameter ratio can more effectively block cracks.

For self-repairing, namely a repairing mode staying in a passive and planned mode, certain disadvantages exist, for example, the effect of later repairing can not be achieved for fine cracks, researches show that the HDCC can realize multi-crack cracking under the condition of shrinkage limitation, the crack width is maintained below 50 mu m, the crack width of the HDCC is controlled below 150 mu m even if the ultimate elongation rate is 1.5-5%, and the crack distance is below 10 mm. Therefore, the traditional concrete crack repair method is not suitable for the micro cracks specific to the HDCC. For these fine microcracks, the repair material should be selected based on the nature of the crack, the width of the crack, and the drying conditions. The majority of inorganic repair materials are hydraulic binders, which contain no or little organic substances, such as polymer cement, have a good repairing effect on macro-cracks in concrete, but are not suitable for dense micro-cracks in HDCC, and also have the defects of high brittleness, high shrinkage, low bonding strength and the like. In the prior art, the following organic repair materials are mainly selected to repair the microcracks: epoxy resin slurry (capable of repairing dry cracks with the width of less than 0.2 mm), nail set (capable of repairing dry fine cracks with the width of 0.03-0.1 mm), propyl set (used for repairing seepage cracks and capable of repairing fine cracks with the width of less than 0.1 mm) and the like. However, these conventional organic repair materials have disadvantages of being easily contaminated, easily aged and exfoliated, and having poor durability. In order to solve the defects of the existing repair materials, a material capable of solving the problems needs to be found.

Manufacturing a high-ductility concrete HDCC test piece:

preparing a high-ductility concrete four-point bending test piece, loading by using an INSTRON 8802 testing machine, controlling the loading according to displacement, wherein the loading rate is 0.5mm/min, the midspan deflection is recorded by an LVDT in real time, preparing cracks in different forms according to the control of different midspan deflections, and measuring the width of the surface crack by using a portable digital electron microscope. The position of the crack to be measured is determined and the crack is then detected with a detector in the microscope. After the initial microcrack width data is obtained, the microcracks are partitioned according to the width, and the repairing effect of the repairing agent for repairing the microcracks in different width intervals is represented.

Three-point/four-point bending and pulling method of test piece. The method adopts a prism beam or a flat plate test piece for testing, and a load is applied to the middle position (three-point bending) or the three-point position (four-point bending), so that a single crack or a plurality of cracks can be generated. In the experimental process, the crack opening displacement is detected through the LVDT, and the load or displacement required by the target crack size is obtained through the load deflection curve calculation. The cracks obtained by the method are V-shaped, the tortuosity and the roughness of the cracks are very close to the crack state under the real condition, and the embodiment also adopts the method to prepare the microcracks in the HDCC

The invention relates to development of an HDCC crack repair material. According to the particularity of the components of the HDCC material and the repairing mechanism of the repairing agent, a novel repairing agent capable of repairing the HDCC micro cracks is researched and prepared. The method comprises the following specific steps: silica sol is used as a main body, sodium aluminate or sodium metaaluminate solution is used as a catalyst, and organic fluorine is used as a wetting agent to prepare the microcrack repairing material. And the repairing agent prepared by the invention is compared with the existing microcrack repairing agent in the prior art in a comparison mode for repairing effect. And measuring the penetration depth of the repairing agent, the repairing effect of the internal and external cracks, the bending strength of the HDCC material after being repaired, and other mechanical properties for comparison.

Cement:

the cement is P.II 42.5R Portland cement (C), which meets the requirements of the national standard GB175-2007 Universal Portland cement.

Fly ash

Class I Class F (low calcium) Fly Ash (FA) was used for the test.

Fine aggregate

Natural river sand (S) is used as the fine aggregate. The detection is carried out according to the GB/T14684-2011 building sand specification, the maximum grain diameter of the sand is 1.18mm, and the fineness modulus is 2.4.

Water (W)

The water used in the embodiment is ordinary tap water.

Fiber

The fiber adopts polyvinyl alcohol fiber (PVAF) made in China.

Additive agent

Two additives were selected for this example: one is polycarboxylic acid high-efficiency water reducing agent (WR), the water reducing rate is more than 20%, and the appearance is light pink powder; the other is a concrete thickener, the main components are silica fume and hydroxypropyl methyl cellulose ether, and the appearance is light gray powder.

Materials required by the repairing agent

The microcrack repairing agent of the invention uses two main repairing materials: one is sodium metaaluminate solution with the mass concentration of 30 to 35 percent; the other is silica sol with the particle size of 10-20 nm and the density of 1.12-1.14 g/cm ³ 。

Preparation of test pieces

This example prepares a finished HDCC four-point bend test piece. Firstly, uniformly smearing demoulding oil on a steel mould, then stirring and forming a sheet test piece with the size of 15mm multiplied by 75mm multiplied by 300mm according to the mixing ratio, flattening, then covering a film, curing for 24h, removing the mould, and carrying out subsequent tests after steaming for two days.

Test piece number description: the test pieces are divided into two groups; the first set of numbers starts with a and is numbered AU, a5, a5-2, depending on the level of preload. U represents the ultimate strength upon loading, 5 represents the loading level of 50%, and 2 represents the second test piece with the loading level of 50%; the second group was similar to the first group, except beginning with B, and was used to study the repair effect of a commercially available repair agent. The fact that two test samples are loaded to 50% of the limit deflection in each group in the test is that in practical engineering application, few HDCC components are repaired when multiple cracks are generated and the limit strength is reached, and therefore the fact that the samples are loaded to 50% of the limit deflection can also provide reference for practical engineering application.

And (3) performing a four-point bending test, wherein the test piece is a thin plate with the dimensions of 15mm multiplied by 75mm multiplied by 300mm, the span is 240mm, the INSTRON 8802 testing machine is used for loading, the loading is controlled according to displacement as shown in figure 1, the loading speed is 0.5mm/min, and the mid-span deflection is recorded by an LVDT in real time.

In order to evaluate the mechanical property of the HDCC material and count the dense microcracks in the HDCC material after the four-point bending test, the test evaluates the bending property of the HDCC material through a load-deflection curve of the HDCC material, observes the surface and internal cracks in the HDCC material after the four-point bending test through a portable digital electron microscope and a CT (computed tomography), and counts the width distribution data of the cracks.

The research on the mechanical properties of the HDCC material mainly comprises the compression property, the uniaxial tensile property and the bending property. The test adopts the bending strength and mid-span deflection of the HDCC material to evaluate the mechanical property of the HDCC material. Wherein the bending stress σ _M ＝FL/(bh ² ) F is bending load in N; l is the span between the test piece supports and is in mm; b is the width of the test piece in mm; h is the height of the test piece in mm.

The mid-span deflection corresponding to the peak load of the test pieces in the group A and the test pieces in the group B are respectively 7.1mm and 7.4mm, the load-deflection curve of the group A, B has an obvious nonlinear section before an initial crack point, and the curve can generate slight jitter along with the slow increase of the load, namely generates slight decrease, then rapidly rises and is continuously repeated, and in the initial stage, the mid-span deflection is gradually increased along with the increase of the load, and the bending stress and the deflection are in a linear relation. When the first microcrack appears, the bending stress is slightly reduced, and the bending stress is increased again because the fibers in the matrix play a role of bridging, so that a tiny peak valley appears on the bending stress-deflection curve. As the load increases, a second microcrack appears, and the fiber bridges the crack again, raising the bending stress again after a slight decrease. Thereafter, the process of "microcracking-fiber bridging-bending stress increase" is repeated, and many minute peaks and valleys are formed on the curve, so that the curve is irregularly jagged. When the width of the main crack develops to a certain degree, the bridging effect of the fiber fails, the load is reduced rapidly, and the test piece is damaged. This indicates that the crack generation of the HDCC material is relatively slow, i.e., not a large number of cracks are generated in a short time with an increase in bending load, but rather, the cracks are gradually generated, and the width of the cracks generated originally increases with an increase in bending load. Therefore, the HDCC material has the characteristics of strain hardening and multi-slit cracking under the action of bending load, has good bending performance and can bear large bending load.

Surface crack

In order to facilitate continuous in-situ monitoring of the same crack after repair, two lines are drawn on two sides of a selected region to be observed respectively, and the crack to be observed is marked and numbered, as shown in fig. 2, only the crack at the marked position is considered during observation of a subsequent repair test. And observing the cracks on the surface of the HDCC test piece by using a portable digital electron microscope. A. The profile of the group B cracks is shown in FIG. 3 and FIG. 4, respectively.

Statistics shows that the number of cracks generated by the HDCC sample with the loading level of ultimate deflection in the marking area is 24 on average, more than 70% of the crack width is concentrated between 60 mu m and 150 mu m, more than 150 mu m of the crack width is about 25%, only few cracks are less than 60 mu m, and the micro cracks smaller than 60 mu m have weak influence on the mechanical property of the HDCC material, so that the HDCC material is not required to be repaired. When the loading level is 50% of the limit deflection. The average number of the cracks is 15, the width of the cracks is 80% and is concentrated between 60 mu m and 150 mu m, the real situation of the HDCC material in practical engineering application can be reflected, and the part of the cracks can influence the mechanical property of the HDCC material, so that the repairing necessity is realized.

Internal cracks

According to the invention, the X-CT is utilized to observe the internal cracks of the HDCC test piece which are not repaired after the four-point bending test. The observation results are shown in fig. 5, 6, 7 and 8.

As can be seen from an X-CT three-dimensional tomography scanning image, the HDCC material generates obvious multi-slit cracking phenomenon after four-point bending. In an X-CT two-dimensional tomography scan image of an HDCC sample, different gray values correspond to substances with different densities, the higher the density is, the larger the gray value is, the lowest the gray value is, holes are formed, and the gray value of the HDCC material is higher. A continuous black gap at the middle position of the X-CT two-dimensional tomography scanning image is a prefabricated crack, and the average depth value of A, B groups of cracks is about 12 mm. Statistics shows that 75% of the internal crack widths of A, B groups of HDCC four-point bending samples are concentrated between 60 micrometers and 150 micrometers, more than 80% of the internal crack widths are concentrated between 100 micrometers and 150 micrometers, the crack volume/total volume ratio of the group A samples is 724/91734, and the crack volume/total volume ratio of the group B samples is 1140/93955, and the control is provided for subsequent tests.

Preparation of silica sol type repairing agent

The HDCC microcrack repairing agent material prepared by the test comprises the following components in parts by weight: 1-2 parts of sodium metaaluminate or sodium aluminate, 100-150 parts of silica sol, 3-5 parts of wetting agent and 100-150 parts of water. The wetting agent is an organic fluorine wetting agent and is one or more of F3030, F3025 and F140, and in the test process, the microcrack repairing material is non-toxic and pollution-free in the preparation and use processes, and belongs to a green environment-friendly product.

In this test, the effect of the sodium aluminate or sodium metaaluminate solution was to accelerate the dispersion of the silica sol in water. The initial value of the mass concentration of the sodium aluminate solution is 30-35%, the initial value of the weight part is 1-2 parts, and through multiple tests, the comprehensive cost and the repairing effect are achieved, the mass concentration is preferably 32-33%, and the mass part is preferably 1.4-1.6 parts; the silica sol has strong permeability, can permeate into the concrete to react with calcium hydroxide in the concrete to generate calcium silicate, forms a film on the surface of the concrete, and has the effects of improving the strength of the concrete and filling cracks. The dispersion medium of the silica sol is preferably water; the initial value of the particle size is 10-20 nm, the initial value of the weight part is 100-150 parts, and through multiple tests, the comprehensive cost and the repair effect are achieved, the particle size is preferably 14-16 nm, and the weight part is preferably 120-130 parts; the density is preferably 1.13 g/cm. The organic fluorine wetting agent is one or more of F3030, F3025 and F140, and when the organic fluorine wetting agent is more than two of them, the proportion of the specific substances in the test is not limited at all, and the substances can be mixed according to any proportion. The initial value of the wetting agent in parts by weight is 3-5 parts, and through multiple tests, the comprehensive cost and the repair effect are preferably 3.8-4.2 parts. The wetting agent can reduce the surface tension of the silica sol after film formation, thereby avoiding the cracking of the silica sol due to overlarge surface tension in the film formation process.

The preparation method comprises the following steps: mixing part of water, a sodium aluminate solution and silica sol to obtain a primary mixed material; in this test, the same parts by weight of the initial mixture portion as those of the silica sol were used, and the mixing order was not particularly limited. Mixing is carried out under the condition of stirring, the rotating speed of stirring is initially set to be 500-1500 r/min, the rotating speed is gradually optimized to be 800-1200 r/min, and finally the rotating speed is set to be 1000 r/min; the stirring time is initially 15-50 min, preferably 20-40 min step by step, and finally is determined to be 25-35 min; after stirring, standing the obtained mixture; the standing time is initially 15-25 min, and after multiple tests, the repairing effect is finally determined to be 18-22 min. During the stirring process, sodium aluminate in the primary mixed material reacts with silicon dioxide in the silica sol to generate aluminum-containing silicate.

After the initial mixing material is obtained, mixing the residual water and the wetting agent, wherein in the test, the sum of the weight part of the residual water and the weight part of the water is the weight part of the water in the technical scheme; the order of mixing the remaining water and the wetting agent is not subject to any particular limitation. The mixing is carried out under the condition of stirring; the stirring speed is initially 100-300/min, preferably 150-250 r/min step by step, and finally 200 r/min; the stirring time is 5-20 min initially, and is preferably 10-15 min gradually. And after stirring, standing the obtained mixture, wherein the standing time is preferably 18-22 min.

And after standing, mixing the primary mixed material and the standing material to obtain the HDCC microcrack repairing material. Mixing is carried out under the condition of stirring, the rotating speed of stirring is initially 500-1000 r/min, and the optimal speed is 600-800 r/min gradually; the stirring time is 5-20 min initially, and is preferably 10-15 min gradually.

After the preparation is finished, the HDCC microcrack repairing material is absorbed by a rubber head dropper for coating, the specific coating process is not limited, and the microcrack repairing material can be uniformly coated on the position to be repaired of the concrete and the coating surface can not have obvious effusion (if the effusion needs to be scraped in time). The coating times are 2-6; after the coating is finished, the coated position cannot be drenched with rain or water within 24 hours, and the effective components of the HDCC microcrack repairing material generate self-crosslinking reaction within the time range of 24 hours.

Preparation of control group epoxy resin type repairing agent

In this test, a commercial product was selected as a control group, and the product was selected to be YBL ⁸⁶ High performance polymeric epoxy sealants. YBL (Yttrium barium copper L) ⁸⁶ The high-performance polymer epoxy resin sealant is composed of epoxy resin and an epoxy curing agent 2, and is formed by curing after being mixed according to a certain ratio (3: 1).

YBL ⁸⁶ The epoxy resin grouting material has convenient and fast mixing proportion and is convenient for field operation. Secondly, the viscosity of the mixture is low. The results of a large number of indoor comparative tests show that the YBL is adopted ⁸⁶ The epoxy resin grouting material has a good effect of treating fine cracks with the width of 0.05mm, and generally can reach more than 98% of the section of the sealed crack. This is very important to improve the ductility and bending strength of HDCC materials.

In this comparative example, an epoxy resin and a curing agent were mixed at a ratio of 3:1, gently stirred with a rubber-tipped dropper, and the mixture was sucked up and applied. The coating process is not limited, the microcrack repairing material can be uniformly coated on the position to be repaired of the concrete, obvious effusion (the effusion needs to be scraped in time) cannot exist on the coating surface, and the coating frequency is 2-6 times. After the coating is finished, the coated position is guaranteed not to be drenched with rain or water within 24 hours. When the polymer epoxy resin repairing agent is applied to a narrow crack, the stress concentration generated at the crack by the shrinkage deformation of cement concrete causes the epoxy resin repairing agent inside the crack to deform, so that the polymer epoxy resin repairing agent plays a role in bonding in the crack.

The test samples were divided into four groups: the first group is cement powder (C); the second group is sample powder (Si-Al) repaired by adding a silica sol repairing agent; the third group is sample powder (Si) to which silica sol was added alone; the fourth group was sample powder (Ep) with epoxy repair agent added. The XRD and FTIR detection results of the four sets of samples are shown in fig. 9 and 10, respectively.

After qualitative analysis is carried out on the XRD pattern, semiquantitative analysis is carried out by using a RIR value method, and the following can be obtained: after the silica sol repairing agent is added, the silica in the silica sol reacts with calcium hydroxide in the cement to generate calcium silicate, and the calcium silicate can form a film on the surface of a concrete crack, so that the strength of the concrete is improved, and the surface of the concrete is sealed. When the epoxy resin repairing agent is added, no new reaction product is generated as can be seen by an XRD pattern.

By analysis of FTIR spectra, vibration frequency (in cm) ^-1 ) 1307 √ k/μ, k is the force constant of the chemical bond, related to bond energy and bond length, and μ is the reduced mass of the diatom. 1900-1200 cm ^-1 Is a double bond stretching vibration area, and can be seen that new functional group silica double bonds are generated after the silica sol repairing agent is added; when the epoxy resin repairing agent is added, the thickness is 1600-1850 cm ^-1 Is a characteristic peak of carbon-oxygen double bond, 2800-3000 cm ^-1 Is a characteristic peak of methyl, 4000-2500 cm ^-1 Is the characteristic peak of X-H (X may be O, N, C, S), and is judged to be the functional group of the epoxy resin repairing agent.

From this it can be concluded that: the repair mechanism of epoxy resin repair agents is to act as a bond in the fracture and not to generate new reaction products to fill the fracture; the silica particles in the silica sol repair agent can then be bound together by different solidification mechanisms, such as gelation and flocculation. Under the gelatinization, the silanol groups on the surfaces of the colloidal particles are subjected to dehydration condensation to form siloxane, and then a three-dimensional network structure is formed. Meanwhile, under the catalytic action of sodium aluminate, the reaction with calcium hydroxide in concrete is accelerated, calcium silicate is generated, and the calcium silicate is used as a repair product, so that cracks can be filled, and the mechanical properties such as bending strength, ductility and the like of the slotted HDCC are improved.

Surface crack

In the test, a group A sample is coated with a test to prepare a repairing agent, a group B sample is coated with a commercial product, and after standing for 24 hours, the surface crack appearance change of the group A, B sample is observed through a portable digital electron microscope and an optical microscope. The results of the digital electron microscope observation of the fracture morphology are shown in fig. 11 and 12. After the silica sol repairing agent and the epoxy resin repairing agent are respectively coated, a plurality of cracks with the width of less than 100 micrometers in the group A test sample are completely filled, the widths of the cracks on the surface of the HDCC test sample with the loading level of limited deflection and the loading level of 50% of the limited deflection in the marking area in the group A are obviously reduced, wherein more than 80% of the cracks are concentrated between 80 and 120 micrometers; after the group B samples are coated with the epoxy resin repairing agent, the repairing effect on the cracks with the width of more than 150 microns before repairing is good, the crack width of HDCC samples with the loading level of limited deflection in the marking area and the loading level of 50% of the limited deflection is obviously reduced, and 80% of the crack width is concentrated between 60 microns and 150 microns.

Internal cracks

The internal crack repairing effect of A, B groups of HDCC samples with cracks after being coated with the silica sol repairing agent and the epoxy resin repairing agent is observed by utilizing an X-ray tomography (X-CT) technology, and the observation results are shown in FIGS. 13, 14, 15 and 16.

As can be seen from an X-CT three-dimensional tomography scanning image, after the HDCC material with four-point bending is repaired by the silica sol repairing agent, the number of internal cracks is obviously reduced, and the silica sol repairing agent can penetrate into the depths of the cracks to generate new repairing substances to fill the cracks; after the four-point bending HDCC material is repaired by the epoxy resin repairing agent, the number of internal cracks is not obviously reduced. In an X-CT two-dimensional tomography scan image of an HDCC sample, different gray values correspond to substances with different densities, the higher the density is, the larger the gray value is, the lowest the gray value is, holes are formed, and the gray value of the HDCC material is higher. As the continuous black gaps in the X-CT two-dimensional tomography map are the prefabricated cracks, the depths of A, B groups of cracks are reduced, and are reduced by 3mm compared with the average depth of 12mm before repair, and the average depth is about 9 mm. Statistics shows that 80% of internal crack widths of the group A HDCC four-point bending samples are concentrated between 50 microns and 110 microns after being repaired by the silica sol repairing agent, only a few cracks (including main cracks) have widths above 150 microns, the ratio of the volume of the crack bodies of the group A samples to the total volume is 270/93272, and is reduced by 63.4% compared with the ratio 724/91734 before repair, so that the repairing mechanism of the silica sol repairing agent mainly generates a new repairing product to fill the cracks, and the repairing effect on the microcracks below 150 microns is obvious; after the group B samples are repaired by the epoxy resin repairing agent, 75% of the crack width is concentrated between 60 mu m and 120 mu m, the volume/total volume ratio of the crack body is 1076/92198, and the crack width is reduced by only 3.8% compared with the ratio 1140/93955 before the repair. Therefore, the epoxy resin repairing agent is used for repairing. Internal cracks in the HDCC specimens still exist, so it was also confirmed that the repair mechanism of the epoxy repair agent does not produce new repair products to fill the cracks, but rather acts as a bond.

The present invention and the embodiments thereof have been described above, and the description is not restrictive, and the embodiments shown in the detailed description are only a part of the embodiments of the present invention, not all embodiments, and the actual configuration is not limited thereto. In summary, those skilled in the art should appreciate that they can readily use the disclosed conception and specific embodiments as a basis for designing or modifying other structures for carrying out the same purposes of the present invention without departing from the spirit and scope of the invention as defined by the appended claims.

Claims

1. The ultra-high performance concrete microcrack repairing agent is characterized in that HDCC microcrack repairing agent materials comprise the following components in parts by weight: 1-2 parts of sodium metaaluminate or sodium aluminate, 100-150 parts of silica sol, 3-5 parts of wetting agent and 100-150 parts of water; wherein the wetting agent is an organic fluorine wetting agent and is one or more of F3030, F3025 and F140.

2. The ultra-high performance concrete microcrack repairing agent according to claim 1, wherein the sodium aluminate or sodium metaaluminate solution acts to accelerate the dispersion of silica sol in water; the initial value of the mass concentration of the sodium aluminate solution is 30-35 percent, and the initial value of the weight part is 1-2 parts.

3. The ultra-high performance concrete microcrack repairing agent according to claim 1, wherein the mass concentration of the sodium aluminate solution is preferably 32-33%, and the mass part is preferably 1.4-1.6 parts.

4. The ultra-high performance concrete microcrack repairing agent according to claim 1, wherein the dispersion medium of the silica sol is preferably water; the initial particle size is 10 to 20nm, and the initial weight is 100 to 150 parts.

5. The ultra-high performance concrete microcrack repairing agent according to claim 1, wherein the silica sol has a particle size of preferably 14 to 16nm and a weight part of preferably 120 to 130 parts; the density is preferably 1.13 g/cm.

6. The ultra-high performance concrete microcrack repairing agent according to claim 1, wherein the organic fluorine wetting agent is preferably 3.8-4.2 parts by weight.

7. The ultra-high performance concrete microcrack repairing agent according to claim 1, wherein the preparation method comprises the following steps:

a: mixing part of water, the sodium aluminate solution and the silica sol to obtain a primary mixed material, wherein the used parts by weight of the part of the water in the primary mixed material are the same as the parts by weight of the silica sol, the mixing sequence is not limited at all, the mixing is carried out under the stirring condition, the stirring rotating speed is initially set to be 500-1500 r/min, the preferable speed is gradually set to be 800-1200 r/min, and finally the speed is determined to be 1000 r/min; the stirring time is initially 15-50 min, preferably 20-40 min step by step, and finally is determined to be 25-35 min; after stirring, standing the obtained mixture; standing for 15-25 min initially, and in the stirring process, reacting sodium aluminate in the primary mixed material with silicon dioxide in the silica sol to generate aluminum-containing silicate;

b: after the initial mixed material is obtained, mixing the residual water and a wetting agent, wherein the sum of the weight parts of the residual water and the weight parts of the partial water is the weight part of the water in the technical scheme; the stirring speed is initially set to be 100-300/min, and the preferable speed is 200 r/min; the stirring time is preferably 10-15 min, after the stirring is finished, the obtained mixture is kept still, and the standing time is preferably 18-22 min;

d: the HDCC microcrack repairing agent is used, the HDCC microcrack repairing agent is uniformly coated on a position to be repaired of concrete, and the condition that obvious effusion cannot exist on a coating surface is ensured; the coating times are 2-6; after the coating is finished, the coated position is guaranteed not to be stained with water within 24 hours, and within the time range of 24 hours, the active ingredients of the HDCC micro-crack repairing agent generate self-crosslinking reaction to repair cracks.